Maybe this is nit-picking, but the slippery slope argument, as it is often used, is a fallacy. Wikipedia has an excellent explanation here: http://en.wikipedia.org/wiki/Slippery_slope
Basically, what is amounts to is that A does not inevitably lead to D. Sometimes there is middle ground to be found at B or C. If you can show that B and C will, without a doubt, occur then it is not a fallacy, but simply assuming A leads to D is.
That's all very well and everything, but HISTORY has shown us ample evidence of this phenomenon in action. Perhaps the timeline is such that step D takes a rather long time to reach. For instance, how many steps and how much time was involved to go from the first gun law affecting gun ownership in 1934 with the federal tax stamp on full automatic weapons to what we have here now today? And I trust you noted my example concerning the income tax laws.
On a more local level, the state permit I have to pay for every year in the state of Florida in order for me to do my business has doubled in the cost, and the forms gotten more complex as the agency responsible requests more and more information every few years, and also places stricter requirements over time as well. Heck, this year for the first time I will need to undergo a hearing test as well as the regular vision test when I go to get my driver's license renewed.
The basic rule of thumb is to assume that EVERY law passed is the first step on a slippery slope. I believe you will be right much more than you will be wrong.